The immune system is the body's primary defense against diseases caused by pathogens, namely bacteria, viruses, fungi etc, as well as against diseases caused by abnormal growth of the body's own cells and tissues (i.e. cancerous tumors). Normally, the immune system is able to distinguish between the body's normal cells or “self” and foreign pathogens or abnormal cells or “non-self”. The processes by which the immune system refrains from reacting to one's own body is called tolerance. Sometimes, the immune system loses the ability to recognize “self” as normal and the subsequent response directed against the tissue or cells, results in loss of tolerance, a state of autoimmunity. The pathologies resulting from autoimmunity often have serious clinical consequences and are one of the major health problems in the world, especially in developed nations.
IL-21 is a potent immunomodulatory four-α-helical bundle type I cytokine that binds to a heterodimeric receptor composed of IL-21R and the common gamma chain (reviewed by Spolski and Leonard, Annu Rev Immunol. Nov. 8, 2007). IL-21 is produced by NK-T and CD4+ T cells (including pro-inflammatory Th17 cells and follicular helper TFH cells that are important for germinal center responses) and has pleiotropic effects on both innate and adaptive immune responses, including enhanced proliferation of B and T cells, increased cytotoxicity of CD8+ T cells and natural killer (NK) cells, differentiation of B cells into immunoglobulin-secreting plasma cells, and regulation of the Th17 cell lineage (see below). IL-21 can also inhibit the antigen-presentation function of dendritic cells and can induce apoptosis in B cells and NK cells under certain conditions. IL-21 has potent anti-tumor activity, but has also been associated with the development of various autoimmune diseases, including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), inflammatory bowel disease (IBD) and psoriasis (reviewed by Spolski and Leonard, Annu Rev Immunol. Nov. 8, 2007).
IL-21 has been shown to modulate antibody responses by directly acting on B cells. (Mehta et al., J. Immunol., 170:4111-4118, 2003; Ozaki et al., Science, 298:1630-1634, 2002; Suto et al., Blood, 100:4565-4573, 2002). IL-21 can induce the differentiation of naïve human B cells into antibody-secreting plasma cells (Ozaki et al. J. Immunol. 173:5361, 2004; Ettinger et al., J Immunol. 175:7867-79, 2005; Ettinger et al, J Immunol. 178:2872-82, 2007; Kuchen et al. J Immunol. 179:5886-96, 2007) and to stimulate the production of IgE in human B cell (Kobayashi et al. Human Immunol. doi:10:1016/j.humimm.2008.10.) In IL-21 or IL-21R deficient animals, fewer antibody-secreting cells are generated from the germinal center reaction and affinity maturation is reduced (Zotos et al., submitted). Extrafollicular antibody forming cells, which are implicated in autoimmunity, require cognate help from a subset of specialized CD4 T cells that secrete IL-21 (Odegard, et al., JEM 205(12):2873-2886, 2008).
Generation of antibodies against allogenic MHC is a pivotal phenomenon in transplant rejection. Transplant recipients who develop titres of anti-MHC antibodies (highly sensitized transplant patients) are t risk for chronic rejection and are poor candidates for new grafts due to likelihood of antibody mediated rejection of the new transplant (Smith, et al., Am J Transplantation 8: 1-11, 2008). In a rat model of acute renal allograft rejection, IL-21 and IL-21R were uniquely increased in intravascular mononuclear cells of renal allografts but not isografts (Hecker, et al., Immunobiology: doi:10.1016/j.imbio.2008.04.004, (2008)). In human cardiac transplants undergoing rejection, expression levels of IL-21 and IL-21R correlate with the ISHLT rejection grade, and highest expression is present in grades 1R and 2R (Baan, et al., Transplantation 83(11): 1485-1492, 2007).
In graft-versus-host-disease (GVHD), the anti-allo response is mediated by uncontrolled activation of T lymphocytes from the graft, which direct an inflammatory response against host tissues. Regulatory T cells (Treg) can modulate this response in animal models. IL-21 has been shown to counteract the regulatory functions of Treg (Clough et al., J Immunol 180: 5395-5401, 2008). In mouse models of GVHD, transfer of IL-21 deficient T cells resulted in significantly reduced clinical signs and histological scores and increased survival, compared with WT T cells. Decreased frequency of IFN-gamma secreting T cells and increased Tregs were observed in the colon mucosa. IL-21 blockade using anti-mIL-21 mAb and WT T cell transfer produced similar results (Bucher et al., Blood (ASH Annual Meeting Abstracts) 2008 112: Abstract #2342).
It has also recently been shown that IL-21 is both produced by and required for the differentiation of mouse pro-inflammatory Th17 cells (Korn et al. Nature. 448:484-487, 2007; Nurieva et al. Nature 448:480-483, 2007; Zhou et al., Nat Immunol. 8:967-974, 2007; Wei et al. J Biol Chem. 282:34605-34610, 2007). Human Th17 cells also produce IL-21 and studies are ongoing to determine whether IL-21 acts as an autocrine factor for human Th17 cells, as it does for mouse Th17 cells. Ozaki et al. (J. Immunol. 173:5361, 2004) demonstrated that IL-21 expression is elevated in lupus-prone BXSB-Yaa mice, a model for systemic lupus erythematosus (SLE), at an age when the early characteristics of autoimmune processes first become evident. Treatment of these BXSB-Yaa mice with a soluble mouse IL-21 receptor (mIL-21R-Fc) partially inhibits various disease parameters, including glomerulonephritis (Bubier et al., Ann N Y Acad Sci. 1110:590-601, 2007). Treatment with mIL-21R-Fc has also been shown to be efficacious in another pre-clinical disease model of SLE, the MRL/lpr mouse (Herber et al. J. Immunol. 178: 3822-3830, 2007), as well as in the collagen-induced arthritis (CIA) model of rheumatoid arthritis (Young et al., Arthr Rheum 56:1152-1163, 2007). Preliminary human data also suggest dysregulation of IL-21 and IL-21R in SLE (Mitoma et al. Int J Mol Med. 16:609-615, 2005; Wang et al., Chinese J. Cell. Mol. Immunol. 23(11):1041-1042, 2007; Sawalha et al. Ann Rheum Dis 67: 458-461, 2008). More recently, Rus et al. data obtained from 24 SLE patients and 15 healthy controls (Nguyen et al., ACR/ARHP Scientific Meeting, 1760/482, 2008 Oct. 24-29 San Francisco, Calif.). Rus et al. showed that 1) IL-21 mRNA expression is significantly increased in CD4+ T cells from lupus patients compared to controls, 2) IL-21 levels are significantly elevated in sera from patients with active compared to inactive SLE or controls, 3) IL-21 enhances CD4+ T cells and CD19+ B cells proliferation in patients and controls in a dose dependent fashion, 4) IL-21 enhances anti-CD40 induced plasma cell differentiation in normal controls and SLE patients, and 5) elevated levels of IL-21 may contribute to proliferation of autoreactive CD4+ T cells and plasma cell differentiation in SLE.
Monteleone et al have demonstrated that IL-21 RNA and protein expression is increased in inflamed but not uninflamed tissue from Crohn's disease (CD) (and, to a lesser degree, ulcerative colitis) patients and that IL-21 production by CD3+ cells from lamina propria mononuclear cells from CD patients is also enhanced (Monteleone et al. Gastroenterology 128:687-694, 2005; Monteleone et al. Gut 55:1774-1780, 2006; Peluso et al., J Immunol 178:732-739, 2007). These authors suggested that IL-21 regulates experimental colitis by modulating the balance between regulatory T cells (Tregs) and Th17 cells (Fantini et al. Eur. J. Immunol. 37:3155-3163, 2007). Inhibition of IL-21 in vivo with a soluble IL-21 receptor in either mouse or rat models of colitis leads to significant reductions in clinical signs of colitis (Young et al. US 2006/0039902).
The IL-21 receptor is expressed by NK cells, and NK cells have been shown to be responsive to treatment with IL-21 both in vivo and in vitro. In oncology patients treated with recombinant human IL-21, altered recirculation patterns in lymphocyte subsets including NK cells, and increased expression of markers of NK cell activation and cytolytic effector capacity were observed (Frederiksen, et al., Cancer Immunol Immunother 57(10): 1439-1449, 2008). In autoimmune diseases, NK cell activity may play a role in promoting inflammation and associated tissue damage. Tissue homing of NK cells is directed by chemoattractants released at the site of inflammation (Morris and Ley, Curr Mol Med.; 4(4):431-8, 2004). Lamina propria NK cells from patients with Crohn's Disease released greater quantities of IFN-γ and TNF-α when stimulated in vitro with IL-21 and IgG, compared with LPNK cells from controls (Liu and Jiu, Chronic Inflammation of Liver and Gut, Falk Symposium abst. No. 163, 2008 Mar. 14-15). NK cells are also reported to regulate autoimmunity and transplant rejection through their interactions with dendritic cells (DC), by killing immature or activated DC, and by releasing cytokines that affect the activation state and antigen presentation functions of the DC (Vivier et al., Nat Immunol 9(5):503-510, 2008; Laffont et al., Blood 112:661-671, 2008). A comparison of peripheral blood mononuclear cells from tolerant and non-tolerant liver allograft recipients showed changes in the transcriptional program of NK cells (Martinez-Llordella et al., J Clin Invest 118(8):2845-2857, 2008). Thus, blockade of IL-21 may modulate the activation status of NK cells, reduce their contribution to tissue inflammation in autoimmune diseases, and alter the clinical course of transplant rejection. NK cells are also reported to regulate autoimmunity and transplant rejection through their interactions with dendritic cells (DC), by killing immature or activated DC and by releasing cytokines that affect the activation state and alter antigen presentation functions of the DC. Thus, blockade of IL-21 may modulate the activation of NK cells and reduce their contribution to tissue inflammation in autoimmune diseases.
The present invention provides anti-human IL-21 monoclonal antibodies and methods of using those antibodies that inhibit the symptoms and biological activities that manifest as autoimmune and inflammatory disorders and are associated with IL-21/IL-21 receptor interactions.